The electrospinning technology is for manufacturing nanofibers. The principle of the electrospinning technology is to provide a driving force generated by an electrical field between a positive and a negative electrodes, so as to overcome surface tension and viscosity of a polymer solution. In addition, streams of polymer solution ejected from a nozzle are mutually repulsive because they carry the same charge; when the solvent evaporates, ultra-thin fibers are formed. The process is also called fiber electrospinning. Comparing with the fibers produced by the prior spinning technology in diameters of several micrometers (μm), the polymeric fibrils produced by the electrospinning technology can achieve a purpose of fiber thinning, due to mechanical and electrostatic forces during the electrospinning process. Moreover, the fabric spun by the electrospinning method enjoys the advantages of having a more favored in higher porosity, larger surface area, and smaller pore size than those of conventional fabrics.
In U.S. Pat. No. 6,616,435, an apparatus of a polymer web formed by an electrospinning process is disclosed. The apparatus comprises: a barrel storing at least one kind of polymer material in a liquid state; a pump pressurizing and supplying the polymer material in the liquid state stored in the barrel; a spinning part for injecting the polymer material in the liquid state supplied by the pump through at least one charged nozzle and manufacturing thin fibers; a high voltage generator providing an electric charge for charging the polymer material discharged through the at least one nozzle of the spinning part to have one polarity; and a collector for piling and transferring the thin fibers to form the polymer web. The electrospinning apparatus has an automatic production ability operated with a plane conveyer belt.
In U.S. Pat. No. 6,110,590, a silk nanofiber composite network produced by forming a solution of silk fiber and hexafluroisopropanol is disclosed. The silk solution has a concentration of about 0.2 to about 1.5 weight percent silk in hexafluroisopropanol, thereby forming a non-woven network of nanofibers having a diameter in the range of about 2 to about 2000 nanometers (nm) for medical use.
In U.S. Publication No. 2003/0211135, a method of producing a composite film fibrous web having diameters averaging less than 100 micrometers by moving nozzles along X-Y axes is disclosed. The resultant product can be applied in, for example, fuel cells and medical supplies.
In brief, the polymeric fibrils can be produced with various diameters by controlling the system parameters of the electrospinning apparatus such as, for example, molecular weight, viscosity, conductivity, surface tension of the polymer solution, controlling operation parameters such as potential of the discharging electrode, flow rate of the polymer solution, the distance between electrodes, and temperature and humidity in the operation environment. However, an uneven web is produced by reciprocating the above nozzle. Reference is made to FIG. 1, which depicts a track of a nozzle on the receiving carrier in the prior art. When the nozzle 101 ejects the polymeric fibrils in a reciprocating way, the receiving carrier goes in a direction 109 vertical to the moving direction of the nozzle. The resultant web is formed with dense polymeric fibrils distributed in a region M and thin polymeric fibrils distributed out of the region M. Reference is made to FIG. 2, which depicts another track of another nozzle on the receiving carrier in the prior art. When the nozzle 101 also ejects the polymeric fibrils in reciprocating way, the receiving carrier goes in a direction 109 vertical to the moving direction of the nozzle. The resultant web is formed with dense polymeric fibrils distributed in a region N and thin polymeric fibrils distributed out of the region N.
In addition to the problem of unevenness in the polymer web produced by the U.S. Pat. No. 6,616,435, there is further an issue of slow production rates for other technologies. For examples, a unit of equipment disclosed in U.S. Pat. No. 6,110,590 is merely an experimental one in the laboratory without continuous production ability. Moreover, the equipment disclosed in U.S. Publication No. 2003/0211135 has a slow production rate for the purpose of uniform distribution. Furthermore, the web produced by such polymeric fibrils produced by the above methods cannot completely satisfy the requirements for thinner diameter, uniform distribution, and higher production rate.
Hence, there is an urgent need for an electrospinning apparatus and method of manufacturing polymeric fibrils, so as to resolve the problems of uneven distribution, slow production rate and so on.